1. Field of the Invention
The present invention relates to the field of door latch and lock mechanisms.
2. Prior Art
Historically, latch bolt mechanisms and dead bolt mechanisms are individual and separate mechanisms, with the latch bolt mechanisms frequently including its own lock. Accordingly, two keys (or alternatively, one key fitting both locks) are required to unlock both the latch mechanism and to withdraw the dead bolt. In the dead bolt mechanism itself, the typical cylinder assembly includes what is commonly referred to as a lost motion drive, which couples the key rotation to the bolt withdrawing mechanism. In particular, a dead bolt is extended or withdrawn by inserting the key into the key slot in the cylinder assembly, rotating the key approximately one hundred eighty degrees toward the locked or the unlocked position as desired, returning the key to the initial position so that the pins and tumblers are again aligned, and then withdrawing the key. Since the key may only be withdrawn when the tumblers and pins are aligned, it is necessary that rotation of the key back to the initial position to allow removal thereof does not undo the effect of the previous key rotation, whether to retract or extend the dead bolt.
To provide the lost motion drive required, the dead bolt mechanism itself is generally driven by a tail piece having approximately 180.degree. of angular freedom with respect to the threaded cap and plug of the cylinder assembly. Accordingly, to extend the latch bolt the key may be inserted and rotated approximately 180.degree. toward the locked position, with the subsequent return to the initial position of the key being decoupled from the latch bolt mechanism. However, on rotation of the key in the opposite direction, immediate drive will be provided to retract the dead bolt, since the mechanism is then at the limit of its lost motion.
One common form of lost motion drive on a cylinder assembly utilizes a key receiving member (e.g., the member containing the tumblers) having the rear or tail section thereof threaded to receive a threaded cap at the inner end of the cylinder assembly. Utilizing threads for this connection allows adjusting the axial position of the threaded cap screwed over the threaded region so as to minimize end play in the assembly, with the threaded cap being retained in position by a spring loaded pin. Retained under the threaded cap is a segment member coupled to a tail piece member, with the segment member occupying an angle of slightly less than 180.degree. and being driven by the pin retaining the threaded cap. It is the combination of the segment member and pin which provides the desired lost motion, with the segment member itself determining the extent of lost motion provided.
In addition to the foregoing, direct drives from the plug and threaded cap have been utilized in prior art locks. By way of example, the Door Lock Mechanism of U.S. Pat. No. 3,933,016, issued Jan. 20, 1976 to Roger J. Nolin and assigned to the assignee of the present invention discloses a latch assembly including a lock having a cylinder assembly driving the mechanism through a gear coupled directly to the plug. Thus, in that assembly, no lost motion of the drive is provided.